Focus indicating devices

ABSTRACT

Focus indicating device for use in optical measuring devices comprises a light source, a condenser lens, a grating provided at its periphery with equidistant and parallel lines and adapted to be moved, an objective lens, an object to be measured and a photoelectric converter element. The grating is located in front of the photoelectric converter element and the light rays emanated from the light source after passing the objective lens, the object to be measured and the grating are impinged on the photoelectric converter element. The grating is moved such that the light rays are traversed by the lines of the grating to generate from the photoelectric converter element a signal for indicating the focal condition of the objective lens.

IPBZIZ United States Patent Kamachi Jan. 1, 1974 FOCUS INDICATINGDEVICES 3,454,772 7/1969 vin, Jr. et al. 250/234 3,542,475 II 1970 2[75] Inventor: Shinichi Kamachi, Tokyo, Japan I Cooper 356/1 6 g OlympusOptical Company Limited, Primary Examiner-John K. Corbin Tokyo, JapanAssistant ExaminerV. P. McGraw [22] Filed: May 17, 1972 Att0rney-Enc H.Waters et al.

4, [21] Appl No 25 313 [*1 ABSTRACT [30] Foreign Application PriorityData Focus indicating device for use in optical measuring devicescomprises a light source, a condenser lens, a May 19, 197] Japan gratingpro ided at per p y q ta and parallel lines and adapted to be moved, anobjective [52] cl 250/201 250/234 527 lens, an object to be measured anda photoelectric converter element. The grating is located in front of 2:'g 59 the photoelectric converter element and the light rays 1 0 0/204237 emanated from the light source after passing the objective lens, theobject to be measured and the grating are impinged on the photoelectricconverter element. [56] [.r References cued The grating is moved suchthat the light rays are tra- UN ED STATES PATENTS versed by the lines ofthe grating to generate from the 2,254,548 9/1941 Ruhle et al. 356/!26photoelectric converter element a signal for indicating 2,818,775 H1958Ullrich 356/126 the focal condition of the objective lens, 3,l75,0933/1965 DeLang 250/237 G 3,520,625 7/1970 Gillieron et al 250/201 4Claims, 11 Drawing Figures PATENTEU JAN 1 4 SHEET 1 [IF 4 F/GJ F IGLZFOCUS INDICATING DEVICES This invention relates to focus indicatingdevices and more particularly to a device for indicating the focuscondition of an objective lens and adapted for use in measuring thedistance between the objective lens and an object to be measured in thedirection of the optical axis without being in contact with the object,for use in indicating the condition that the objective lens is in focus,and for use in autofocussing the objective lens, that is, automaticallyfixing the objective lens at its true focal point.

In a microscope for use in, for example, optical measuring devices, ithas been the common practice to use an objective lens having a lowmagnification in the order of SXs to lOXs, and as a result, theallowable range of the focus of the objective lens is so wide that it isdifficult to fix the focus of the objective lens at its true focalpoint.

As a focus indicating device in which the focus of the objective lens isdetermined without visual aids, it has heretofore been proposed toprovide a photoelectric converter element such as a CdS layer upon whichsurface is produced the image of an object to be measured through anobjective lens and the photoelectric signal obtained from the CdS layeris used to indicate the focus condition of the objective lens. Suchknown focus indicating device is simple in construction, but has thedisadvantage that the focus of the objective lens can not accurately beindicated and, as a result, it can not be applied to optical measuringdevices. A further disadvantage is that highly accurate indications ofthe focus of the objective lens can not be obtained even if use is madeof a complex and expensive construction.

It is an object of the invention to provide a focus indicating devicewhich is simple in construction and is capable of reliably andaccurately indicating the focal condition of the objective lens in acomparatively easy manner.

This and other desirable objects are attained, according to theinvention, by a focus indicating device comprising a light source, acondenser lens, a grating provided at its periphery with equidistant andparallel lines and adapted to be moved, an objective lens, an object tobe measured, and a photoelectric converter element, the arrangementbeing such that the light rays emanated from said light source passthrough said condenser lens, grating, objective lens and the surface ofsaid object and impinge on said photoelectric element, said gratingbeing located in front of said photoelectric converter element and movedsuch that said light rays are traversed by the lines of said grating,thereby generating from said photoelectric converter element a signalfor indicating the focal condition of said objective lens.

This and other features of the invention are described in greater detailin the following description of certain embodiments. This descriptionrefers to the accompanying drawings, in which:

FIG. I is a diagrammatic illustration of one embodiment of a focusindicating device according to the invention;

FIG. 2 is a plan view of a first rotatable grating;

FIG. 3 is a plan view ofa second fixed grating suitable for use incombination with the first rotatable grating shown in FIG. 2;

FIG. 4 is a wave form of a photoelectric signal generated from thephotoelectric converter element when the objective lens is in focus;

FIG. 5 is a wave form of a photoelectric signal generated from thephotoelectric converter element when the objective lens is not in focus;

FIG. 6 is a diagrammatic illustration of another embodiment of the focusindicating device according to the invention suitable for use inautofocussing devices;

FIG. 7 is a diagrammatic illustration similar to FIG. 6 but showing analternate version of the second fixed grating;

FIG. 8 is a diagrammatic illustration of another embodiment of the focusindicating device according to the invention suitable for use infinders;

FIG. 9 is a diagrammatic illustration of a further embodiment of thefocus indicating device according to the invention in which use is madeof one rotatable grating;

FIG. 10 is a diagrammatic illustration of a variant of FIG. 9 in whichuse is made of one vibrating grating; and

FIG. 11 is a plan view showing the vibrating grating shown in FIG. 10.

Referring to FIG. 1, element 1 is a light source, element 2 is acondenser lens, element 3 is a first rotatable grating, element 4 is amotor for rotating the rotatable disc semitransparent mirrors 3, 5 and6, element 7 is an objective lens, element 8 is an object to bemeasured, element 9 is a second fixed grating, element 10 is aphotoelectric converter element, and element 1 l is an eyepiece.

In FIG. 2 is shown an example of the construction of the first grating3. As shown in FIG. 2, the first grating 3 comprises a transparent discprovided along its periphery with a number of close equidistant andparallel opaque lines 3 each arranged in a radial direction and adaptedto be rotatable around the center axis. FIG. 3 shows an example of theconstruction of the second grating 9. As shown in FIG. 3, the secondgrating 9 comprises a transparent sector provided along its peripherywith several close equidistant and parallel opaque lines 9' eacharranged in a radial direction and adapted to be fixed.

The light rays emanated from the light source 1 pass through thecondenser lens 2 and impinge on the first grating 3. The image ofthefirst grating 3 is produced through the semitransparent mirror 5 andobjective lens 7 on the surface of the object 8. The image of the firstgrating 3 thus produced on the surface of the object 8 is producedthrough the objective lens 7 and semitransparent mirrors 5 and 6 on thesurface of the second grating 9. The light rays passed through thesecond grating 9 are impinged on the photoelectric converter element 10.

If the first grating 3 is rotated by the motor 4 and the focus of theobjective lens 7 is accurately fixed on the surface of the object 8, anideal triangular photoelectric signal shown in FIG. 4 is generated fromthe photoelectric converter element 10. In FIG. 4, the lowest value ofthe triangular signal is black level which is zero level in the idealcase, while the highest value of the triangular signal is the brightestlevel.

If the first grating 3 is rotated by the motor 4 and the focus of theobjective lens 7 is not fixed on the surface of the object 8, that is,the image of the first grating 3 is not in focus, the corrugated waveform photoelectric signal shown in FIG. 5 is generated from thephotoelectric converter element 10.

As a result, the suitable treatment of the photoelectric signalgenerated from the photoelectric converter element is capable ofobtaining a signal for indicating the focus condition of the objectivelens 7. For example, the photoelectric signal generated from thephotoelectric converter element 10 may be treated in a manner such thatthe alternating current component of the photoelectric signal generatedfrom the photoelectric converter element 10 is rectified into a directcurrent component which is converted into a focus indicating signal. Asseen from a comparison between FIGS. 4 and 5, if the focus of theobjective lens 7 is correctly adjusted such that the focus of theobjective lens 7 is accurately fixed on the surface of the object 8, thealternating current component of the photoelectric signal becomes verylarge as shown in FIG. 4 and, as a result, a large rectified directcurrent output can be obtained. On the contrary, if the focus of theobjective lens 7 is slightly displaced from the surface of the object 8,the alternating current component of the photoelectric signal becomesvery small and, as a result, a very small rectified direct currentoutput can be obtained.

Moreover, if the focus of the objective lens 7 is accurately fixed onthe surface of the object 8, the photoelectric signal from thephotoelectric converter element 10 becomes triangular in wave form asshown in FIG. 4, while if the focus of the objective lens 7 is displacedfrom the surface of the object 8, the photoelectric signal from thephotoelectric converter element 10 is deprived of higher harmoniccomponents and hence approaches a fundamental sine wave as shown in FIG.5. Thus, it is possible to supply the photoelectric signal to aband-pass filter adapted to pass higher harmonics, for example, a thirdharmonic and the third harmonic output of the band-pass filter may beused as a signal for indicating focus.

In the embodiment shown in FIG. 1, the light rays emanated from thelight source 1 pass through twice the air space between the objectivelens 7 and the surface of the object 8 so that the change of thephotoelectric signal from the photoelectric converter element 10 becomesconsiderably large when the objective lens 7 is not in focus, therebysignificantly improving the sensitivity of indicating the focuscondition of the objective lens 7.

The above-mentioned way of indicating the focus condition of theobjective lens 7 may simultaneously be effected in case of measuring theenlarged image of the surface of the object 8 by means of the objectivelens 7 and eyepiece 11. In this case, the light rays emanated from thelight source 1 do not prevent the measurement of the surface of theobject 8 by means of the objective lens 7 and eyepiece 11. This isbecause of the fact that the first grating 3 rotated at a speed fasterthan a suitable speed is capable of viewing the image of the firstgrating 3 without flickering of light resulting from the residual imageeffect.

The light rays emanated from the light source land reflected by thesurface of the object 8 are partly reflected by the semitransparentmirror 6 and impinged on the second grating 9 to form Moire patternthereon. Thus, the present embodiment is capable of accuratelyindicating the focus condition of the objective lens 7 irrespective ofthe presence of local indentations on the surface of the object 8.Moreover, since the light rays emanated from the light source 1 passthrough the objective lens 7 per se of the microscope (TTL system), thefocus condition of the objective lens 7 can be indicated in an extremelyaccurate manner.

As stated hereinbefore, the focus condition of the objective lens 7 canbe indicated by treating the photoelectric signal from the photoelectricconverter element 10. In this case, the photoelectric signal from thephotoelectric converter element 10 is supplied to a meter whoseindicator needlejndicates the condition that the objective lens 7 is infocus.

The magnification of the objective lens 7 of the microscope for use inoptical measuring devices is often low so that the allowable range ofthe focus of the objective lens 7 is wide and, as a result, it isdifficult to fix by naked eyes the focus of the objective lens 7 at itstrue focal point on the surface of the object 8. As stated hereinbefore,the invention renders it possible to fix accurately the focus of theobjective lens 7 at its true focal point by indicating the focalcondition with the aid of the meter.

Moreover, the use of the output from the photoelectric converter element10 insures generation of the signal for indicating the focus conditionof the objective lens 7, and further provides the important advantagethat the focus indicating signal can adjust the microscope body tube andcontrol a servomechanism for adjusting the focal position of theobjective lens 7, thereby effecting automatically the keeping of theobjective lens 7 in focus.

In such autofocussing devices, it is necessary not only to keep theobjective lens 7 in focus, but also to detect whether or not the focusof the objective lens 7 is displaced forwards or rearwards from its truefocal point. In order to detect such forward or backward displacement ofthe focus from its focal point, the second grating 9 is provided at itsfront side with a glass plate 12 adapted to elongate the light ray pathand provided at its rear side with two photoelectric converter elements10, 10 as shown in FIG. 6. The focus indicating light rays reflected bythe semitransparent mirror 6 are impinged through the second grating 9on one of the photoelectric converter element 10 and are impingedthrough the glass plate 12 and the second grating 9 on the otherphotoelectric converter element 10'. In the present embodiment, thesecond grating 9 is located at a'position between the position of theback focus of the objective lens 7 reflected by the semitransparentmirror 6 (dotted lines) and the position of the back focus of theobjective lens 7 reflected by the semitransparent mirror 6 and extendedby the glass plate 12 (dotted lines). The provision of the twophotoelectric converter elements 10, 10' and the glass plate 12 resultsautomatically in that when the outputs from the photoelectric converterelements 10, 10' become equal to each other a signal showing that theobjective lens 7 is in focus is generated and also is capable ofdetecting the displacement of the objective lens 7 from its true focalpoint. For this purpose, the outputs from the photoelectric converterelements 10, 10' are supplied to a signal treating circuit 13 thattreats the outputs in a suitable manner to generate a focus indicatingsignal which is supplied to a servomechanism 14 adapted to adjust thedistance between the objective lens 7 and the object 8, with the resultthat the focus of the objective lens 7 can automatically and accuratelybe fixed at the surface of the object 8 in the well known technique.

Another possible embodiment of the autofocussing device which permits ofdetecting the displacement of the focus of the objective lens 7 from itstrue focal point is shown in FIG. 7. in this embodiment, the secondgrating 9 is divided into two grating portions 9 and 9' which aredisplaced along the optical axis and the light rays passed through thesecond grating portions 9 and 9' are impinged on the two photoelectricconverter elements l0, respectively. The back focus of the objectivelens 7 is located at a point between the second grating portions 9 and 9as shown by dotted lines in FIG. 7. The condition that the outputs fromthe two photoelectric converter elements 10, 10' are equal each othershows that the objective lens 7 is in focus. The comparison between thetwo outputs from the two photoelectric converter elements 10, 10'permits of detecting the displacement of the focus of the objective lens7 from its true focal point in a forward or backward direction.

As stated hereinbefore, the output from the photoelectric converterelement 10 or elements l0, 10 can be treated to obtain a signal forindicating the focus of the objective lens 7 and the signal can beutilized to continuously measure the distance from the object 8 to theobjective lens 7 in a direction of the optical axis without touching theobject 8. When the object 8 is disposed on a movable table (not shown)and the object 8 is moved to be scanned by the light rays, the focusindicating signal is used to adjust the distance between the objectivelens 7 and the object 8 such that the focus of the objective lens 7 isfixed on its true focal point on the surface of the object 8. Thedistance between the objective lens 7 and the object 8 may be measuredby a suitable means to detect the height of the object 8 in a directionperpendicular to the object 8.

The present embodiment may be applied to a conventional photoelectricmicroscope provided with a slit or pinhole and adapted to dispose theobject 8 on a table movable in X and Y directions and hence move theobject 8 together with the table in X and Y directions to be scanned bythe slit or pinhole and to generate a photoelectric signal for detectingthe end face position of the object 8. In such case, the table movablein X and Y directions is capable of obtaining the X and Y co-ordinatesof the object 8 and the output of the photoelectric converter element 10makes it possible to obtain 2 co-ordinate of the object 8 as describedabove, and the provision of a low-pass filter adapted to pass a lowfrequency which is lower than the frequency for operating the focusindicating device permits of detecting the end face position of theobject 8-.

In FIG. 8 is shown another embodiment of the focus indicating deviceaccording to the invention. In the present embodiment, the light raysemanated from the light source I pass through the condenser lens 2 andimpinge on the first grating 3 formed by a part of a cover glassdisposed on the object 8. The image of the first grating 3 is producedon the surface of the second grating 9 by means of the objective lens 7and the light rays passed through the second grating 9 are impinged onthe photoelectric converter element 10. In the present embodiment, thefirst grating 3 is made fixed while the second grating 9 is maderotatable and is rotated by means of the motor 4. The objective lens 7,second grating 9 and photoelectric converter element 10 are enclosed ina casing 16 which is detachably secured to a microscope body tube 17enclosing an objective lens 7' and eyepiece 11 therein. The distancefrom the objective lens 7 to the surface of the object 8 is made equalto the distance from the objective lens 7 of the microscope to thesurface of the object 8. The focus indicating device according to thepresent embodiment plays a role of a finder which can accurately fix thefocus of the objective lens 7' of the microscope at the surface of theobject 8. The first grating 3 is described as is formed by the coverglass, but such construction is not always necessary. The first grating3 per se may also be disposed on the object 8.

In FIG. 9 is shown a further embodiment of the focus indicating deviceaccording to the invention. In the present embodiment, provision is madeof one rotatable grating 18 through which are passed two times the lightrays. That is, the light rays emanated from the light source 1 areconcentrated by the condenser lens 2 upon the rotatable grating 18driven by the motor 4. The image of this grating 18 is produced throughthe semitransparent mirrors 6, 5 and objective lens 7 on the surface ofthe object 8. The light rays reflected by the surface of object 8 areimpinged through the objective lens 7, semitransparent mirror 5 and areversing prism 19 on the surface of the rotatable grating 18, with theresult that the image of the rotating grating 18 produced on the object8 is produced again on the rotating grating 18. The direction ofrotation of the image produced on the rotating grating 18 is opposite tothe direction of rotation of the rotating grating 18, and as a result,the light rays passed through the rotating grating 18 and impinged onthe photoelectric converter element 10 is capable of giving a focusindicating signal which is the same as that generated by the abovementioned embodiments.

FIG. 10 shows a variant of the embodiment shown in FIG. 9, in whichprovision is made of a grating 20 adapted to be vibrated in a'directionperpendicular to the plane of the drawing. The grating 20 is made of arectangular transparent plate and provided at its upper and lower edgesthereof with close equidistant and parallel opaque lines 20' and drivenby a driving device 21 is directions shown by arrows in FIG. 1 1. Thelight rays emanated from the light source 1 pass through the condenserlens 2 and impinge on the vibrating grating 20. The image of thevibrating grating 20 is produced through the semitransparent mirrors 6,5 and objective lens 7 on the surface of the object 8. The ight raysreflected by the object 8 are impinged through the objective lens 7,semitransparent mirror 5 and reversing prism 19 on the vibrating grating20. The direction of vibration of the image of the vibrating grating 20produced on the vibrating grating 20 is opposite to the direction ofvibration of the vibrating grating 20, and as a result, the light rayspassed through the vibrating grating 20 are impinged on thephotoelectric converter element 10, thereby generating a signal forindicating the focus condition of the objective lens 7.

The embodiments of the invention shown in the drawings is for thepurpose of describing the objects and features of the invention. It isto be understood, however, that modifications, changes and alterationsmay be made without departing from the scope and spirit of theinvention.

What is claimed is:

l. A device for indicating the focus of an objective lens of amicroscope while observing the image of an object to be tested throughthe objective lens, which comprises a microscope including an eyepiece,an objective lens and an object to be tested; and an optical systemconstituting a part of said microscope and including a light source, acondenser lens, a grating having upper and lower half portions providedwith equidistant and parallel opaque lines and a photoelectric converterelement, said grating being rotated'at a speed faster than the residualimage effect of eyes, whereby the light rays emanated from said lightsource and passed through said condenser lens is impinged on the upperhalf portion of said grating whose image produced on the object to betested is impinged on the lower half portion of said grating to form aMoire pattern thereon and the correct focus position of said objectivelens is indicated by the output signal of said photoelectric converterelement when the contrast of said Moire pattern becomes maximum withoutpreventing the observation of the surface of the object to be tested bysaid microscope.

2. A focus indicating device as claimed in claim 1 wherein said gratingconsists of a first movable grating and a second fixed grating and thelight rays emanated from said light source after passing through saidfirst movable grating are reflected by the surface of said object andimpinged through said second grating on said photoelectric converterelement.

3. A focus indicating device as claimed in claim 2 wherein said secondgrating is provided at its front side with a glass plate adapted toelongate said light ray path and provided at its rear side with twophotoelectric converter elements, said light ray path being passedthrough said second grating to one of said two photoelectric converterelements and passed through said glass plate and said second grating toanother photoelectric converter element, the outputs from said twophotoelectric converter elements being supplied to a signal treatingcircuit whose output is supplied to a servomechanism adapted to controlsaid objective lens.

4. A focus indicating device as claimed in claim 2 wherein said secondgrating is divided into two grating portions each of which is providedat its rear side with a photoelectric converter element, said light raypath being passed through said two second grating portions to said twophotoelectric converter elements, the outputs from said twophotoelectric converter elements being supplied to a signal treatingcircuit whose output is supplied to a servomechanism adapted to controlsaid objective lens.

* I! 1 I i

1. A device for indicating the focus of an objective lens of amicroscope while observing the image of an object to be tested throughthe objective lens, which comprises a microscope including an eyepiece,an objective lens and an object to be tested; and an optical systemconstituting a part of said microscope and including a light source, acondenser lens, a grating having upper and lower half portions providedwith equidistant and parallel opaque lines and a photoelectric converterelement, said grating being rotated at a speed faster than the residualimage effect of eyes, whereby the light rays emanated from said lightsource and passed through said condenser lens is impinged on the upperhalf portion of said grating whose image produced on the object to betested is impinged on the lower half portion of said grating to form aMoire pattern thereon and the correct focus position of said objectivelens is indicated by the output signal of said photoelectric converterelement when the contrast of said Moire pattern becomes maximum withoutpreventing the observation of the surface of the object to be tested bysaid microscope.
 2. A focus indicating device as claimed in claim 1wherein said grating consists of a first movable grating and a secondfixed grating and the light rays emanated from said light source afterpassing through said first movable grating are reflected by the surfaceof said object and impinged through said second grating on saidphotoelectric converter element.
 3. A focus indicating device as claimedin claim 2 wherein said second grating is provided at its front sidewith a glass plate adapted to elongate said light ray path and providedat its rear side with two photoelectric converter elements, said lightray path being passed through said second grating to one of said twophotoelectriC converter elements and passed through said glass plate andsaid second grating to another photoelectric converter element, theoutputs from said two photoelectric converter elements being supplied toa signal treating circuit whose output is supplied to a servomechanismadapted to control said objective lens.
 4. A focus indicating device asclaimed in claim 2 wherein said second grating is divided into twograting portions each of which is provided at its rear side with aphotoelectric converter element, said light ray path being passedthrough said two second grating portions to said two photoelectricconverter elements, the outputs from said two photoelectric converterelements being supplied to a signal treating circuit whose output issupplied to a servomechanism adapted to control said objective lens.